The present disclosure relates to conveyance control systems, and particularly to a controller for pneumatic conveyance of dry granular materials.
Dry, loose, granular materials, sometimes referred to as dry bulk materials, and referred to herein as ‘dry commodities’ or ‘commodities’, include materials such as grain, shredded or chopped vegetation, plastic pellets, and dry chemical, food, or other pellets, flakes, and powders. Commodities are often moved between storage, processing, and transport equipment using a pneumatic conveyance system.
Pneumatic conveyance systems for handling grain after it is harvested is an example of such systems. There are different types of grain dryers, but one typical design includes one or more heated grain columns in which grain is feed into the top and is exposed to heat as it slowly flows downward in the vertical column. The discharged at the bottom of the column is generally rate controlled to provide the desired level of drying, resulting in a desired moisture content of the grain. For example, a metering roll is generally used to control the release of the grain out of the bottom of the drying column. The grain released by the metering roll then generally drops into and is carried away by a discharge auger.
Such dryers are generally controlled by a PLC or other control device that monitors temperatures of the heating plenum and grain, and that controls the burners, metering rolls, and auger accordingly to provide a preset moisture content of grain being discharged. A metering roll speed signal is also generally provided by such a dryer control device. The signal is proportional to the rate of discharge of the grain from a grain drying column. For example, if the grain is too wet, a slower discharge speed will be used and allow more time for drying. As the grain is dried, the discharge speed will be increased, and will typically continue to vary. Such changes in speed are reflected in the discharge speed signal, which may be, for example, an analog signal varying between 0 to 10 volts.
In many systems, the discharge auger is connected to a pneumatic conveyance system that is used to transport the grain to other equipment, for example storage or transport bins. Pneumatic conveyance systems move the grain through a pipe under the pressure of air forced through the pipe by a blower fan driven by a motor. A motor driven airlock allows grain to enter the pipes without letting the pressurized airflow escape. Conventional pneumatic conveyance systems used for grain transport typically have 3 to 6 inch pipes and use a single speed blower motors that runs at full speed, for example, 1750 rpm, regardless of how much grain is introduced into the system. Because of the single speed, a vent in the system is used to bleed off excess air flow/pressure to the atmosphere.
If more pressure than is needed is provided to the pipes, the air wasted by venting off the excess represents higher than required energy costs. Additionally, if commodity is driven to too high a velocity, damage to the commodity can result, especially at bends in pipes or upon transfer into a transport vehicle, lower the value and/or usefulness of the commodity.